1. Field of the Invention
The present invention relates to front opening unified pods, or FOUPs, and in particular to FOUPs which include mechanisms for preventing the FOUP door from being improperly inserted into the FOUP.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles and molecular contaminants become of interest.
FOUPs are in general comprised of a vertically oriented FOUP door which mates with a FOUP shell to provide a sealed, ultraclean interior environment in which wafers may be stored and transferred. The wafers are supported either in a cassette which may be inserted into the shell, or to shelves mounted to the interior of the shell.
In order to transfer wafers between a FOUP and a process tool within a wafer fab, a pod is typically loaded (either manually or automatedly) onto a load port on a front of the tool so that the pod door lies adjacent the port door of the process tool. Thereafter, latch keys within the port door engage a latch assembly within the FOUP door to decouple the FOUP door from the FOUP, and at the same time couple the FOUP door to the port door. Details relating to such a latch assembly within a pod door are disclosed for example in U.S. Pat. No. 4,995,430, entitled xe2x80x9cSealable Transportable Container Having Improved Latch Mechanismxe2x80x9d, to Bonora et al., which patent is owned by the assignee of the present application. The assembly disclosed therein includes a two-stage latching operation to securely latch a pod door to a pod shell as shown in prior art FIGS. 1 and 2A-2B. The latch assembly is mounted within the pod door, and includes a latch hub 28 which engages first and second translating latch plates 30. The port door includes a pair of latch keys that extend into slots 13 formed in the latch hub to thereby rotate the latch hubs clockwise and counterclockwise. Rotation of each latch hub 28 will cause translation of the first and second latch plates 30 in opposite directions.
FIG. 1 is a front view of an interior of the pod door illustrating the latch assembly in the first stage of the door latching operation. When a pod door is returned from its engagement with the port door to the pod, the latch keys within the port door rotate the latch hub 28 to thereby translate the latch plates 30 outwardly so that latch fingers 14 on the distal ends of the latch plates 30 extend in the direction of arrows A into slots 15 formed in the pod shell. The slots 15 conventionally include a transverse wall 17 formed in the pod shell which divides the slot generally in half. The fingers 14 include a space 19 which aligns over the wall 17 when the fingers 14 are received within the slots 15.
FIG. 2A is a side view through line 2xe2x80x942 of the latch assembly shown in FIG. 1, and FIG. 2B is a side view as in FIG. 2A but illustrating the second stage of the door latching operation. In particular, the latch hub 28 further includes a pair of ramps 40 so that, after the fingers 14 have engaged within the slots 15 of the pod shell, further rotation of the hub causes the proximal ends 32 of the latch plates engaged with the hub to ride up the ramps. This causes the latch plates to pivot in the direction of arrows B, about axes lying in the plane of each latch plate and perpendicular to the direction of latch plate translation. The effect of this pivoting during the second stage is to pull the pod door tightly against the pod shell to thereby provide a firm, airtight seal between the pod door and shell.
In order to separate a pod door from a pod shell, as when a pod is initially loaded onto a load port interface for wafer transfer, mechanisms within the port door engage the rotatable hub 28 and rotate the hub in the opposite direction than for pod latching. This rotation disengages the latch fingers 14 from the pod shell and allows separation of the pod door from the pod shell.
The Semiconductor Equipment and Materials International (xe2x80x9cSEMIxe2x80x9d) standard relating to FOUP doors requires that the positions of the door mounting features, i.e., the rotatable latch hubs, the fingers on the latch plates and the slots in the FOUP shell, be symmetrical about a horizontal axis. The authors of the standard believed it would be convenient to allow the FOUP door to be inserted into the FOUP right side up or up side down. However, as it turns out, this symmetry of the mounting mechanisms about the horizontal axis provides a significant disadvantage as explained with reference to FIG. 3.
FIG. 3 shows a FOUP 20 housing a plurality of wafers 21. The FOUP door 22 is conventionally provided with a plurality of protrusions 23 defining a plurality of recesses 24 therebetween. The position of the protrusions 23 and recesses 24 are precision controlled so that upon insertion of the FOUP door 22 into FOUP 20, the wafers 21 within the FOUP seat within recesses 24 to prevent the wafers 21 from getting dislodged. However, if the FOUP door is inserted up side down, the wafers 21 may not align within recesses 24, and instead the protrusions 23 may contact the wafers 21. This is true because in a conventional FOUP, a distance X between a top wafer and the top interior surface of the FOUP is different than a distance Y between the bottom wafer and the bottom interior surface of the FOUP, and thus the position of the protrusions and recesses are not symmetrical about the horizontal axis. Contact between the protrusions on the port door and the wafers can result in damage and/or destruction of each of the wafers within the FOUP. Thus, for 300 mm semiconductor wafers, an improper seating of the FOUP door in the FOUP can result insignificant monetary losses.
The error in loading a FOUP door into a FOUP up side down frequently occurs when the FOUP door is manually returned to an empty FOUP. For example, after FOUPs go through a cleaning process, technicians often manually return the FOUP door to the FOUP. FOUP doors are currently marked with an indicator as to which is the top and bottom side of a FOUP door. However, this marking is often overlooked or not understood when a FOUP door is manually inserted into the FOUP.
The empty FOUP including the up side down door is subsequently transferred to a load port. As indicated above, conventional load ports operate to transfer the FOUP door to and from the FOUP regardless of whether the door is up side down or right side up. Thus, upon arrival at the load port, the up side down FOUP door is removed as usual and wafers are loaded into the FOUP. However, upon the subsequent return of the FOUP door to the FOUP by the load port, the up side down door is driven into contact with the wafers, and damage and/or destruction of the wafers can occur.
It is therefore an advantage of the present invention to provide a system for preventing FOUP doors from improper insertion into a FOUP.
It is a further advantage of the present invention to provide a mechanical system which physically blocks a FOUP door from being improperly inserted into a FOUP thereby preventing damage to the wafers therein.
It is another advantage of the present invention to provide a mechanical system for preventing improper insertion of a FOUP door into a FOUP without altering or adding to the outer edges or surfaces of a sealed FOUP.
These and other advantages are provided by the present invention in which the size, shape and/or location of the latch plate fingers and corresponding slots at the top edge of the FOUP are different than the latch plate fingers and corresponding slots on the bottom edge of the FOUP. Thus, unless the FOUP is correctly oriented right side up upon insertion of the door to the FOUP, the door will not properly fit into the FOUP. Thus, when a sealed FOUP is received at a load port to receive wafers, the FOUP door is right side up and the danger of wafer damage due to an up side down FOUP door is removed.